1. FIELD
This invention relates to the provision of automatic machinery for the filling of containers, such as bottles, with flowable substances ranging from very thin to extremely viscous, and including substances which readily form suds or foam.
In particular my invention is directed to overcoming problems in the prior art peculiar to the dispensing of extremely viscous substances.
2. PRIOR ART
The closest prior art of which I am aware is disclosed in my United States Pat. Nos. 3,870,089, which issued Mar. 11, 1975; and 4,095,628, issued June 20, 1978.
Nearly all the principles and features disclosed in those two patents are operative in the system of my present invention, with only two exceptions--both arising from the peculiarities of extremely viscous products. As noted in those prior patents, the principles and features there disclosed are directed to dispensing products ranging from quite thin to quite viscous. The products which are the motivation for the present invention, by contrast, are outside that range--being "extremely" viscous.
As explained in my U.S. Pat. No. 3,870,089, very accurate volumetric filling requires a cyclically operating volumetric metering device, close control of liquid at all points in the system downstream of the metering device, and close control of air or other gas which is or might be in the system. In addition, as also explained in that patent, very accurate filling requires close monitoring of system operation to guard against partial fills, very clean operation, and finally, for a multiple-head filling machine, operation of all the heads under as nearly as possible identical conditions.
These principles are implemented by the following techniques, which are general background for the present invention: (1) a submersible dispensing nozzle which fills deep within the bottle, and which has (2) a closure device at its tip and (3) a device for sucking up drops of the fluid from the nozzle--but only when the tip is out of the body of the fluid; (4) positive-pressurized operation of the entire system at all times, (5) isolation of the product-dispensing ducts and chambers from any pneumatic control system, (6) positioning the nozzle above the volumetric chamber, (7) a bubble-entrapment device upstream of the volumetric chamber; (8) sensors and interlocks to monitor and control system cycling; and (9) individual flow-rate adjustment for each head, and (10) common volume adjustment for all the heads.
Four other devices for implementing the principles enumerated above are particularly pertinent to the improvements of the present invention: (1) a biacting piston, (2) solid, positive mechanical stops for defining the ends of the piston travel within the volumetric chamber, (3)individual volume adjustment for each head, and (4) complementarily formed adjacent end-walls of the chamber and piston, at the bottom of the chamber and piston respectively, which act cooperatively to squeeze gas bubbles toward a port of the chamber so as to eliminate them from the system within the first few cycles of operation. These four features, like those mentioned in the preceding paragraph, were described in my U.S. Pat. No. 3,870,089. The principles which give rise to these four devices are just as important with extremely viscous products as with others, and the first three of the four remain useful, with modifications, in implementing the principles.
Referring to FIG. 2 of my U.S. Pat. No. 3,870,089, note that positive mechanical stopping action at the bottom of the piston stroke is provided by engagement of the lower surface 27b of the piston 27 with the lower internal surface 26c of the chamber 26; and the positive mechanical stopping action at the top of the piston stroke is provided by engagement of the actuator 27f, carried by piston rod 27e, with the pneumatic switch button 30a. In the latter case, the positive mechanical stopping action does not actually occur until the button "bottoms out" (or, as drawn, "tops out") against the inner end of the cavity provided for the button action in the switch body 30.
Pneumatic control signals for reversal of the piston 27 at the bottom of its stroke are generated by engagement of the actuator 27f with the button 29a of pneumatic switch 29; and such signals are generated at the top of the stroke by engagement of the actuator 27f with the previously mentioned switch button 30a. Both limit switches 29 and 30 are adjustable with respect to the cylinder 26.
Since lower limit switch 29 performs solely the reversing function while lower positive stop action is provided by the chamber end-wall 26c, the point at which the reversing signal occurs is inherently adjustable with respect to the point at which the positive mechanical stop is engaged. By contrast, since the upper limit switch 30 performs both the reversing function and the positive mechanical stop function, the reversing signal is not adjustable with respect to the mechanical stop. The fact of this nonadjustability becomes crucial in relation to extremely viscous products, as will be explained below.
Other prior-art systems generally lack the basic context of the present invention, namely the combination of automatically reversing dispensing systems with biacting pistons and positive stops. For example, the system of Buford et al., disclosed in U.S. Pat. No. 3,447,281, issued June 3, 1969, discloses a biacting piston and limit switches for reversing the piston; however, the switches themselves are not positioned to halt the piston. Overtravel of the piston with respect to the switches is intended, as may be seen from the drawings, and reliance is placed entirely on the reversing signals, with no provision for operative positive mechanical stops. One of the points in Buford's specification where this fact appears is at column 11, lines 48 through 57, where it is stated, "When the piston reaches the right end of its travel, the enlargement 49 at the left end of the piston rod opens valve 204 to . . . admit a pneumatic signal . . . to . . . halt the filling operation . . . . "
As to the bubble-expulsion technique mentioned above, the prior art other than my U.S. Pat. No. 3,870,089 does not appear to address itself to any comparable matter, since the prior art generally is not concerned with precision levels at which expulsion of bubbles is significant.
My U.S. Pat. No. 4,095,628 points out two additional principles and their implementations, improving on my earlier system:
(1) A five-port, four-way valve used to control product flow in two different paths simultaneously, thereby reversing the flow connections to the biacting volumetric cylinder, can be simplified to a four-port valve by using an internal passageway formed within the valve spool.
(2) Foaming products are best dispensed with a variable-speed system--high flowrate for filling the parts of each container where foaming is least problematical, and lower flowrate for filling the parts of the container where foaming is most serious.
(The second principle is implemented by a timed constriction of the flow path between the product supply and the dispensing nozzle. In some cases the constriction is carried by the volumetric piston itself, on a spring which projects in front of the piston, and so is brought into operation only when the piston is within a particular distance of the end of its stroke.)
The simplified valve remains useful with extremely viscous materials. The principle and implementation of the two-speed system are independent of the extreme-viscosity case, and can be used either separately from or in conjunction with the extreme-viscosity provisions of the present invention. It may be noted, however, that relatively few products are both foaming and extremely viscous; and, moreover, that extremely viscous products move through the dispensing system so slowly that foaming tendencies tend to be suppressed without use of slower speeds at critical points in the fill.
My U.S. Pat. No. 4,095,628 is not addressed to the matter of bubble expulsion, but rather to foaming control speed variation. However, it is significant to note the speed-variation device illustrated in FIG. 2 of that patent is not readily compatible with the bubble-squeezing structure in FIG. 2 of my earlier patent. Therefore it is necessary to choose, in practicing my heretofore disclosed inventions, between foaming control through speed variation and bubble removal. My present invention provides bubble removal in a manner which is at least in principle compatible with speed variation as shown in FIG. 2 of my U.S. Pat. No. 4,095,628.
In attempting to design, make and use the systems of my U.S. Pat. Nos. 3,870,089 and 4,095,628 with extremely viscous substances to be dispensed, I have noted small imprecisions of initially unexplained origin.
Although the imprecisions involved were rather small, it is important to bear in mind the context of systems of this type. Under the law, packaging companies must fill each container with at least as much fluid as is nominally contained--i.e., as the label indicates. Therefore, whatever imprecision is present in a dispensing system must all be "placed," so to speak, above the nominal value; that is to say, the packager, not the consumer, must absorb the economic impact of any imprecision. Of course the requirement that every customer receive at least a nominal fill is properly founded in the concern for consumer protection; while the objectionability of significant overfill, in some industries, is compounded by the undesirability of waste per se--from an ecological or natural-resources conservation point of view.
Hence the importance of maintaining, with extremely viscous products as well as with less-viscous ones, the precision level indicated in my first-mentioned patent--1/28 ounce, or roughly five drops, per gallon, or 0.03%.